vector algebra form

[mjskay]

More musings: maybe this really needs to turn into more of a vector algebra... e.g. vectors of layers. Because what you really want to be able to do for something like this is have two layers: the densities and the lines, add densities to [0, lines] and do blend("clear") on the second element (so maybe something like densities + c(0, lines) |> c(1, blend("clear"))...